Blushing

Blushing is the involuntary reddening of a person's face due to embarrassment or emotional stress, though it has been known to come from being lovestruck, or from some kind of romantic stimulation. It is thought that blushing is the result of an overactive sympathetic nervous system. Severe blushing is common in people who suffer social anxiety in which the person experiences extreme and persistent anxiety in social and performance situations.

Girls blush, sometimes, because they are alive,
Half wishing they were dead to save the shame.
The sudden blush devours them, neck and brow;
They have drawn too near the fire of life, like gnats,
And flare up bodily, wings and all.

The apple blossoms' shower of pearl,
The pear tree’s rosier hue,
As beautiful as woman's blush,
As evanescent too.

Letitia Elizabeth Landon, The London Literary Gazette (5th April 1823), 'April'. Also included in The Vow of the Peacock (1835)

Such was the colour—when her cheek
Spoke what the lip might never speak.
The crimson flush which could confess
All that we hoped—but dared not guess.
That blush which through the world is known
To love, and to the rose alone—